Use smoke in polymer and polymer_expressions.

pkg/polymer/test/prop_attr_reflection_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:html';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'package:polymer/polymer.dart';
 
 class XFoo extends PolymerElement {
   XFoo.created() : super.created();
 
   @observable var foo = '';
   @observable String baz = '';
 }
 
 class XBar extends XFoo {
   XBar.created() : super.created();
 
   @observable int zot = 3;
   @observable bool zim = false;
   @observable String str = 'str';
-  @observable Object obj;
+  // TODO(sigmund): change this type to Object (see dartbug.com/16962)

[Siggi Cherem (dart-lang), 2014/02/21 03:55:13]

FYI - I managed to revert this workaround (I made a more general workaround in
_toType in smoke.mirrors)

+  @observable var obj;
 }
 
 class XCompose extends PolymerElement {
   XCompose.created() : super.created();
 
   @observable bool zim = false;
 }
 
 Future onAttributeChange(Element node) {
   var completer = new Completer();
@@ skipping 75 matching lines @@
       expect(xbar.attributes.containsKey('zim'), false, reason:
           'attribute reflects false valued boolean property as NOT '
           'having attribute');
       xbar.obj = 'hi';
     }).then((_) => onAttributeChange(xbar)).then((_) {
       expect(xbar.attributes['obj'], 'hi', reason:
           'reflect property based on current type');
     });
   });
 }